Aluminum base alloys



Patented Sept. 18, 1951 ALUMINUM BASE ALLOYS Charles B. Willmore,Aurora, 111., assignor to William F. Jobbins, Incorporated, Aurora,111.,

a corporation of Illinois No Drawing. Application April 12, 1949,

. Serial No. 87,109

5 Claims. 1

This invention relates to aluminum base alloys, and it has particularreference to the improvement in castability of aluminum base alloys, asmeasured by reduced surface shrinkage and less porosity in the casting.It also relates to the improvement in other physical properties of analuminum base alloy containing zinc, copper and silicon as majoralloying elements.

Aluminum base alloys of the type described have been used in themanufacture of castings.

They have not achieved wide commercial acceptance because they do nothave desirable casting characteristics and their physical properties arenot sufficiently superior to other commercial alloys having moredesirable casting properties. One of the principal difficulties suffered by these alloys resides in the inability of securing an acceptableproduct by sand casting or by casting in permanent molds. planation,when the cast molten alloy cools down through the liquids range, thechange from a liquid state to a solid state does not occur immediately.Instead, crystals or nuclei are formed which grow into a matrix havingmicroscopic voids caused by the decrease in volume of the liquid as itassumes crystalline form. The voids that are formed are called poreswhen of small dimension and Widely distributed, or pin holes, if thevoids collect in certain areas.

These voids constitute low pressure areas and unless they are quicklyfilled, the casting surfaces may actually collapse to form depressedareas,

characteristicof surface shrinkage, accompanied by undesirable crystalstructure. Collapse to form surface shrinkage usually occurs in regionsIn the event cult to handle when casting about a core in permanentmolds. Their inferior casting characteristics cause undesirable stickingof the core. This oftenleads to the destruction of the casting andexcessive damage to the mold.

It is an object of this invention to provide an aluminum base alloyhaving improved castability when cast in sand or permanent molds.

Another object is to formulate for improvements in castability and otherphysical properties in an alloy composed chiefly of aluminum and By wayof eX-' 2 containing silicon, copper and zinc as major alloyingelements.

A further object is to provide an aluminum base alloy characterized byimproved physical properties and improved castability when compared toalloys of corresponding composition heretofore produced.

Still another object is to provide a heat treatable aluminum base alloycontaining silicon, zinc and copper as major alloying elements andcharacterized by improved castability and strength when fabricated bysand or permanent mold casting methods.

A still further object is to produce an aluminum base alloy havingphysical properties which may be improved by solution heat-treatment andwhich may be further improved by artificial ageing; said alloy alsobeingcharacterized by improved castability not secured by thecorresponding alloy without the additions of chromium, manganese andtitanium.

I have found that by the addition of a small amount of chromium to analuminum base alloy, castability of the alloy in sand or permanent moldsis markedly improved. It is believed that the chromium, either by itselfor in combination with the other elements of the alloy provides forsufficient liquid medium to fiow through available open channels to fillthe voids and microscopic spaces left within the matrix of crystalsformed by the freezing metal and produce substantially completesoundness in the solidified structure. Thus, by the almost immediatefilling of the voids by a molten metallic component, the low pressureareas developed are eliminated and the danger of collapse of the castingsurface or the development of porosity is greatly minimized, or entirelyavoided. It is undesirable to have too much of the liquid metalliccomponent at this stage, because the molten metal might then occupy thegreater proportion of the alloy and its characteristics will predominatein the casting. When this condition prevails, the alloy is said to behotshort because the liquid has insufficient strength to maintain theintegrity of the freezing mass.

The desired relationship for'effectively reducing shrinkage and porosityof the casting, whether fabricated by sand casting or by permanent moldor chill casting, is achieved when chromium is present in the alloy inconcentrations ranging from 0.05 to 1.0 by weight, while best use ismade of 0.10 to 0.45 percent by weight of chromium.

While it is conceivable that chromium may have this desirable effect onany aluminum base alloy, it is especially applicable to aluminum basealloys containing silicon, zinc, and copper as alloying elements andparticularly when the alloying elements are present in amounts rangingfrom 2 to 4 percent copper, 2 to 8 percent zinc and 2 to 8 percentsilicon, and the total of iron and nickel impurities are maintainedbelow 0.75 percent.

castability can best be determined by comparative tests made with apattern that is difli- ,cult to cast without shrinkage. By such test,improvement in shrinkage secured in both sand and permanent mold castingby the addition of chromium to an aluminum base alloy containing zinc,and copper alloy as major alloying elements, and iron, nickel and up to0.15 manganese as impurities, is shown in Table I.

TABLE III Effect of manganese on physical properties of aluminum basealloy TABLE I In addition to the improvement in castability ChemicalComposition of Alloying Elements, Amount of Shrinkage in Per Cent ZincCopper Silicon Chromium Sand Casting fi g gg A 5. 4-5. 5 2. 9-3. 19 5.4-5 5 B 5. 4-5. 2. 9-3. 1 5. 4-5 5 0.10 C 5. 4-5. 5 2. 9-3. 1 5. 4-5 5O. D 5. 4-5. 5 2. 9-3. 1 5. 4-5 5 0.45

Impurities 0.46 iron, 0.04 nickel, 0.15 manganese.

Ordinarily it has been considered that grain refinement occasioned bythe addition of grain refining substances has the tendency to giveimproved castability. While this concept may be correct in someinstances, it will be significant that this relationship does not existwith respect to the improvement of castability of analuminum-silicon-copper and zinc alloy. In fact, the addition ofchromium in the amounts by which castability is notably improved causesan increase in grain size, while the addition of titanium, a grainrefining element, to the aluminum base alloy without chromium willfurther increase the degree of shrinkage and porosity, as will beapparent from Table IV.

Castability and physical properties may be improved when additionalmanganese, over and above that existing as impurity is substituted inwhole or in part for chromium. To get comparable effects however it isdesirable to use greater amounts of manganese. For example, it isnecessary to use as much as 0.6 percent manganese to achieve theimprovement in castability secured by the addition of 0.1 to 0.25percent chromium. However, more manganese, up to at least 1.5 perbyalloying with chromium, I have discovered that improvements in physicalproperties are also secured, especially when titanium is incorporatedwith the chromium and/or manganese. Titanium in amounts greater than0.20 percent is seldom used and best results are secured when titaniumis present with the elements for improving castability in amounts from0.05 to 0.15 percent. The improved characteristics may constitute acooperative relationship wherein castability of a desired character isinfluenced by the presence of chromium and manganese in the prescribedamounts, and any harmful effects resulting from the use of these metalsare more than fully compensated by the addition of titanium. In fact,the product secured by the addition of both chromium and titanium hasphysical properties which are better in most instances than those whichcharacterize the corresponding compositions with only one of theelements or in complete absence of either of the elements, as shown bythe following Tables IV and V.

cent can be tolerated in the alloy with increas- TABLE IV in enefi s.

g b t TABLE, II Sand cast Eflect of manganese on castability of aluminumA C F F 7 base alloys containing about 5.5 percent zinc, 6O 3.0 percentcopper and 5.5 percent szlzcon as Zinc m 5M5 Mrs-5 My mayor alloyingelements C0pper 2. 0-3.1 2.9-3.1 2.0-3.1 2. 0-3.1 Silicon 5.4-5.55.4-5.5 5.4-5.5 545.5 ghromium. 0. 2(5) 0.25 Chemical Com ositionitanium 0.10 0.10 in Percen l; Amount of shrinkage Grain Size, mm. diam1.43 1.06 0. 77 1. 25

Impurities Man- Sand Permanent Shrinkage gig Heavy Slight ganesc CastingMold Iron Nickel AS Gist: t 1 25 500 20 00 200 5 u timates rengt1 ,5 252 ,300 15 Heavy fg? yield strength 131000 13,000 1 11500 14, 000 0 40004 030 Veryslight Slight mam-Gated: 46 61 N Db ultimate strength 32,000 33, 700 31, 400 34,500 Medium-1 yield strength 10,000 10, 300 17,80017,700 70 04 Sn ht Heat Treated and Aged, ulti- 0170 mate strength 10,200 46,900 40,400 51,000

TABLE V Permanent mold cast Grain Size, mm. diam 0. 45 0. 52 0.42 0. 37

Shrinkage Medium Very Slight Slight to Very Slight Medium As Cast:

ltimate 30, 000 30, 900 29, 300 30, 100

yield 13, 450 12, 400 14, 300 Heat Treated:

ultimate 36, B 38, 400 40, 300 39, 800

yield 16, 400 16, 900 17, 600 19, 400 Heat Treated and Aged,

ultimate 50, 100 49, 200 53, 700 55, 600

Impurities 0.46 iron, 0.04 nickel, 0.15 manganese. I Ultimate strengthand yield strength are given in lbs. per sq. inch.

As used in the tables, the term heat treated refers to solution heattreatment of the casting for 6 hours at 935 to 945 F. followed byquenching in hot water. Heat treatment time may be extended or shorteneddepending upon the weight of the casting, and heat treatment may becarried out at lower temperatures with a corresponding increase in time.The term aged" refers to artificial ageing of the heat treated castingto precipitate out elements or compounds put into solid solution duringheat treatment.

Artificial ageing in the tested compositions was carried out by exposureof the heat treated casting to 305 to 315 F. for about three hours.

It will be observed that chromium and in most instances manganese hasthe effect of increasing grain size without appreciable loss in theexcellent casting characteristics secured by the addition of chromiumalone.

In practically every instance the ultimate strength of the casting isincreased by the addition of chromium, while the yield strength remainsubstantially unchanged. The combination of chromium and titanium givesultimate strengths and yield strengths which exceed, by a large amount,any of the values secured by the addition of either of the elementsalone. Exceptional results in this respect are secured in the heattreated and aged alloys. In practically every instance the yieldstrength, ultimate strength and castability are improved by the additionof manganese.

A very decided advantage is observed in the use of my new alloy inpermanent mold casting. The alloy sets more rapidly in the mold with theconsequent desirable advantage in that the molding cycle can be greatlyshortened. For example, in one operation, a casting formed with my alloycomposition can be removed after 1 to 1 minutes in the mold, while acorresponding composition without chromium or chromium and titaniumrequires a setting time of 1 to 2 minutes. This enables the shorteningof the time cycle by about percent. Furthermore, the reduced shrinkageoccasioned by the improved casting characteristics of the alloy permitscasting in permanent molds without the difficulties heretoforeoccasioned upon casting about a core.

It will be apparent from the description that I have produced a new andimproved aluminum base alloy containing zinc, copper and silicon, whichalloy has greatly improved castability as measured by shrinkage andporosity and also has considerably better physical properties. The alloycorresponding to my invention is an alloy having desirable physicalproperties which may be improved by solution heat treatment and may befurther improved by artificial ageing at relatively low temperatures.

It will be understood that changes may be made in the ratio of materialsand compositions within the limitations prescribed and their method oftreatment without departing from the spirit of the invention, especiallyas defined in the following claims.

What is claimed is:

1. An aluminum base alloy consisting essentially of approximately from 2to 4 percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon andfrom 0.05 to 1.00 percent chromium the remainder being aluminum withless than 0.75 percent impurities in the form of iron and nickel.

2. An aluminum base casting alloy consisting essentially of from 2 to 4percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon, 0.05 to1.00 percent chromium and from 0.05 to 0.20 percent titanium theremainder being aluminum with less than 0.75 percent impurities in theform of iron and nickel.

3. An aluminum base casting alloy consisting essentially of from 2 to 4percent copper, 4 to 8 percent zinc, 2 to 8 percent silicon and 0.10 to0.45 percent chromium, the balance being aluminum with less than 0.75percent impurities in the form of iron and nickel.

4. An aluminum base casting alloy consisting of from 2 to 4 percentcopper, 4 to 8 percent zinc, 2 to 8 percent silicon, 0.10 to 0.45percent chromium, and 0.05 to 0.15 percent titanium, the balance beingaluminum with less than 0.75 percent impurities made up of iron andnickel.

5. An aluminum base casting alloy consisting essentially of from 2 to 4percent copper, 2 to 8 percent zinc, 2 to 8 percent silicon, and anelement selected from the group consisting of 0.05 to 1.00 percentchromium, 0.15 to 1.5 percent manganese and mixtures thereof, the restbeing aluminum with less than 0.75 percent impurities made up of ironand nickel.

CHARLES B. WILLMORE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,572,489 Johnston et a1 Feb. 9,1926 2,098,081 Bates Nov. 2, 1937 2,280,170 Stroup Apr. 21, 19422,290,016 Bonsack July 14, 1942 2,511,551 Smith et al June 13, 1950FOREIGN PATENTS Number Country Date 723,417 France Apr. 8, 1932 OTHERREFERENCES Manual of Aluminum Casting Alloys, published by the AluminumResearch Institute, Chicago, 1947, page 26.

Metals Handbook published by the American Society for Metals, 1948 ad,page 840.

1. AN ALUMINUM BASE ALLOY CONSISTING ESSENTIALLY OF APPROXIMATELY FROM 2TO 4 PERCENT COPPER, 2 TO 8 PERCENT ZINC, 2 TO 8 PERCENT SILICON ANDFROM 0.05 TO 1.00 PERCENT CHROMIUM THE REMAINDER BEING ALUMINUM WITHLESS THAN 0.75 PERCENT IMPURITIES IN THE FORM OF IRON AND NICKEL